feat: respect backup list filter option

src/cli/backup.rs

@@ -131,7 +131,12 @@ impl BackupListArgs {
     pub fn run(&self, cli: &Cli) -> io::Result<()> {
         let meta = cli.meta()?;
 
-        for (name, manager) in meta.managers().iter() {
+        // A bit scuffed? Sure
+        for (name, manager) in meta
+            .managers()
+            .iter()
+            .filter(|(name, _)| self.layer.is_none() || &self.layer.as_ref().unwrap() == name)
+        {
             println!("{}", name);
 
             for chain in manager.chains().iter().filter(|c| !c.is_empty()) {